In the manufacture of cigarette filter rod, it is common practice to apply a plasticizer, e.g., triacetin to a tow band of filter material such as cellulose acetate preliminary to actually enclosing the filter material in a wrapper thus to form a filter plug structure, such plug structure being formed in a continuous stock thereof in known manner with known plug forming apparatus. The plasticizer is applied to promote selective adhesion of the fibers of the cellulose acetate at points of crossing to give a cohesive structural character to the fiber mass. The plasticizers used in such operation generally can be classed as relatively low flash point liquids so that it is desirable that they not be stored and supplied and used in the rod making operation at relatively high temperature. For example, in the case of triacetin, it has a flash point of about 280.degree. F., and it is recommended that it not be subjected to storage temperatures over 100.degree. F. Moreover, a proper supplying of the triacetin to the application operation requires that the plasticizer have a relatively constant viscosity for uniform pumping from a source to the application operation and that the viscosity be such at the transfer device, e.g., dip and transfer rolls, which actually apply the plasticizer to the tow band. To maintain viscosity relatively constant at the plasticizer source it is required that the temperature at such source be maintained relatively constant. In practice this is difficult to achieve because the pump for conveying plasticizer to the application device as well as external heat souce devices used in the overall rod forming operation transfer heat to the plasticizer, the last-mentioned including, e.g, the high velocity blower supplying air to the banding jets. Furthermore, it is common to return unused plasticizer from the application operation to the source thereof, which return plasticizer flow tends to increase the temperature of the plasticizer at the source. If the plasticizer heats up unduly, it will become less viscous and possibly require adjustment to the applicator device to insure proper quantities thereof are transferred to the tow band -- an undesirable condition as it impedes manufacturing efficiency. Similarly, too high a temperature will not permit enough plasticizer to adhere to a transfer roll because of very low viscosity unless the roll speed is substantially increased. This again is undesirable. Accordingly, it is desirable that the temperature and hence viscosity of the plasticizer used in a cigarette filter rod forming operation be controlled relatively precisely to insure optimized operation of the filter rod forming apparatus, other than by heating excessively as in past practice.